Time to man up dad, you need to be the best you can be for your daughter, not the sky is falling waiting on egg shells for the EX to do something you MIGHT freak out about.
It seems like the only thing that has really been damaged is your ego and that probably stings the most. I get the impression you never in a million years thought this could happen to you?
Listen, my STBX is banging a married dude, so what? I don't want to be with her anymore and the fact that your ex has moved on shows she doesn't want to be with you. Sucks, trust me I'm there, but the time to figure that out has passed. You can continue to trip on things behind you or face front and live the rest of your life on your terms. You are divorced, i'm assuming you have an agreeable parenting plan with your child and your health. Stop looking at the glass as half empty.
You spend a lot of time thinking about the ex, how are you going to change that? When people talk about not disturbing your peace in that first year, your first order of business is to stop thinking about what the ex thinks about things, why she does things the way she does, all of it. She is no longer any of your concern and you can't control things you have no control over, so stop poising yourself and by extension, your child.